The foreign secretary is abroad as MPs vote on a third runway at Heathrow - an issue he’s been passionate about in the past, even threatening to lie down in front of a bulldozer if one were to be built.

On Sunday, a colleague challenged him to “put his money where his mouth is” and resign over his opposition to the scheme, while Sarah Wollaston said his absence from the vote “won’t wash”.

Johnson defended his absence in a letter to local councillors in his constituency - Uxbridge and South Ruislip - which the Evening Standard obtained.

“I have long been an opponent of a third runway at Heathrow and that is why I am not voting for it tonight,” he said.

“I have made clear my opposition since joining the government, and I will continue to lobby colleagues from within government. Some of my critics have suggested that I should resign over the issue. No doubt they have my best interests at heart.

“But it is clear from what is likely to be a large majority of MPs who are in favour of a third runway that my resignation would have achieved absolutely nothing. Hillingdon council have been emphatic that they would rather have me in the cabinet and fighting for their cause on this and other issues.”

His absence meant he was able to avoid a choice between voting against Heathrow expansion on a three-line whip, which would have meant quitting as Foreign Secretary, or supporting the Government in order to keep his job.